Can you try that :
//myWindow beeing the popup
myWindow.document.write("<br><br>" + myWindow.opener.document.location.href + "")
Update
If you cannot get the popup window object you can pass the url of the calling window in the query string :
radopen('urlOfThePopup.aspx?opener=' + document.location.href, ...)
Then in your popup code
<%=Request.Querystring("opener")%>